X-ray mammography based on film-screen or Xeroradiographic detection is commonly accepted as a mass screening technique for breast disease. A certain risk is associated with this examination since X-ray radiation is also ionizing and dedicated X-ray equipment is often required.
More recently, broad beam light sources (sometimes referred to as "light torches") with a wide spectral bandwidth in the visible and infrared have been used to examine the breast. The broad beam transmitted through the breast is usually recorded by a video camera, converted to an analog signal and viewed on a video monitor or digitized and analyzed on a computer. The ability to discriminate between various tissue-types in the breast is poor due to the wide spectral bandwidth of the transmitted beam. Resolution is lost since a large amount of scattered light is transmitted from the breast to the detector.
Lesion sizes that are detectable with this approach have generally been no smaller than what the physician can detect by palpitation. Resolution is far below that which can be obtained with X-ray imaging systems.
We realize that a collimated light source of narrow spectral bandwidth (such as generated by a Laser) could be used to produce a beam or a number of beams of very small spatial dimensions. The small spatial dimensions of the beam could be used to obtain images of the breast with high spatial resolution, whereas the narrow spectral bandwidth would improve the characterization of the composition of the breast material being imaged to be more detailed. More information could be obtained by acquiring additional images at other wavelengths of light again, with narrow spectral bandwidths.
Although not essential to the invention disclosed, a desireable imaging format would be to have the collimated light beam(s) incident normal to the surface of the breast and to exit from the breast normal to the breast surface. The breast could be placed between two transparent plates and compressed so as to establish good surface contact and at the same time reducing the path length through the breast of the transmitted light beam(s). The compression technique is commonly employed in X-ray mammography.
The light entering and exiting from the plate-breast-plate system could undergo additional collimation so as to reject much of the scatter component. Collimation can be accomplished through use of masks, as for example of the checkerboard type. The whole object is imaged by moving the mask such that all points to be imaged are scanned.